What Lowers Vitamin A in the Body?

Worldwide, between 250,000 and 500,000 children who are vitamin A-deficient become blind every year. For adults, understanding what lowers vitamin A in the body is crucial, as depletion can stem from various health conditions, lifestyle choices, and even genetic factors, not just a poor diet.

Quick Summary

Vitamin A depletion can occur due to inadequate dietary intake, impaired absorption from gastrointestinal diseases, and reduced storage capacity caused by liver disorders. Other factors include coexisting nutrient deficiencies, infections, certain medications, and genetic variations affecting metabolism.

Key Points

• Malabsorption Disorders: Conditions like celiac disease, cystic fibrosis, and Crohn's disease damage the intestines, preventing proper absorption of fat-soluble vitamin A.

• Liver Dysfunction: The liver stores 50-80% of the body's vitamin A, so diseases like cirrhosis or alcohol-related damage severely impair storage and release.

• Zinc Deficiency: Adequate zinc is required for synthesizing retinol-binding protein (RBP), which transports vitamin A, and for converting retinol into its active form.

• Chronic Alcohol Use: Excessive alcohol consumption depletes vitamin A by damaging the liver and interfering with the enzymatic pathways that process the vitamin.

• Medication Interactions: Certain drugs, including the weight-loss medication Orlistat and some antibiotics, can interfere with vitamin A absorption.

• Genetic Variations: Variations in genes such as BCO1 can decrease the body's efficiency in converting beta-carotene from plant-based foods into active vitamin A.

Core Reasons for Low Vitamin A Levels

Vitamin A is a fat-soluble nutrient essential for vision, immune function, and cellular growth. While insufficient dietary intake is a primary cause, especially in developing countries, a combination of medical and lifestyle factors can dramatically reduce levels even with a sufficient diet. A severe drop in serum retinol levels, the active form of vitamin A circulating in the blood, doesn't happen until the body's substantial liver reserves are nearly exhausted.

Medical Conditions Affecting Absorption

Several chronic diseases disrupt the body's ability to absorb or utilize vitamin A, which is a fat-soluble vitamin. These conditions interfere with the normal digestive and absorptive processes in the gut and liver.

• Chronic Gastrointestinal Disorders: Diseases such as celiac disease, Crohn's disease (a type of inflammatory bowel disease), and cystic fibrosis can all lead to malabsorption. These conditions damage the lining of the small intestine or affect the production of digestive enzymes, which are vital for breaking down and absorbing fats and fat-soluble vitamins like vitamin A.
• Pancreatic Insufficiency: The pancreas produces enzymes essential for fat digestion. Conditions like chronic pancreatitis or cystic fibrosis can lead to pancreatic insufficiency, meaning a lack of these enzymes, causing poor fat and vitamin A absorption.
• Liver Disorders: The liver is the body's main storage organ for vitamin A, holding 50-80% of the body's total reserves. Chronic liver diseases such as cirrhosis or alcohol-related liver damage can severely impair the liver's ability to store, convert, and transport vitamin A effectively, leading to depletion even if intake is adequate.
• Bile Duct Obstruction: Bile is produced by the liver and stored in the gallbladder, playing a crucial role in fat digestion. A blockage in the bile ducts prevents bile from reaching the small intestine, leading to malabsorption of fats and fat-soluble vitamins.

Dietary and Lifestyle Factors

• Poor Overall Nutritional Status: Severe or prolonged malnutrition, especially protein-energy malnutrition, can deplete vitamin A. The body needs protein to synthesize retinol-binding protein (RBP), which transports vitamin A from the liver to tissues. Without enough protein, this transport mechanism fails, even if liver stores are sufficient.
• Zinc and Iron Deficiency: These mineral deficiencies can impair vitamin A metabolism. Zinc is a critical component of several enzymes involved in vitamin A transport and conversion, including the synthesis of RBP in the liver and the conversion of retinol to retinal in the eye. A lack of iron can also hinder vitamin A metabolism.
• Chronic Alcohol Use: Alcoholism significantly interferes with vitamin A metabolism and storage. Excessive alcohol consumption damages the liver's ability to store the vitamin and impairs the conversion of retinol to its active forms.
• Low-Fat and Restrictive Diets: As a fat-soluble vitamin, vitamin A requires dietary fat for proper absorption. Severely restrictive low-fat diets can compromise absorption, leading to deficiency over time. Vegans, who consume only provitamin A carotenoids, may also be at risk if their diet is not carefully planned and they have genetic predispositions for poor conversion.

Infections and Medication Interactions

• Frequent Infections: High rates of infection, particularly common childhood illnesses like measles and chronic diarrhea, can deplete vitamin A reserves and increase physiological needs. The body utilizes vitamin A more rapidly during infections to support immune function, creating a vicious cycle where a deficiency weakens the immune response, making one more susceptible to subsequent infections.
• Surgical Procedures: Bariatric surgery or other intestinal bypass surgeries can reduce the surface area of the small intestine available for nutrient absorption, increasing the risk of malabsorption and subsequent vitamin A deficiency.
• Medications: Several types of drugs can lower vitamin A levels. For example, the weight-loss medication Orlistat (Alli, Xenical) can decrease the absorption of fat-soluble vitamins. Certain antibiotics like neomycin and bile acid sequestrants can also interfere with absorption.

Genetic Factors

Genetic variations can influence how efficiently the body absorbs and processes vitamin A, potentially contributing to lower levels. For example, single nucleotide polymorphisms (SNPs) in the BCO1 gene can affect the conversion of beta-carotene from plant sources into the active form of vitamin A, retinol. Other genes, such as RBP4 and TTR, influence the transport of vitamin A throughout the body.

Factors that Deplete vs. Inhibit Vitamin A

Factor	How It Lowers Vitamin A	Impact on Absorption, Storage, or Utilization
Chronic Liver Disease	Damages liver cells, impairing the organ's ability to store vitamin A and produce transport proteins.	Primarily affects storage and mobilization from reserves.
Gastrointestinal Diseases (e.g., Celiac, Crohn's)	Inflammatory damage to the intestinal lining hinders nutrient uptake.	Primarily impairs absorption from the diet.
Zinc Deficiency	Reduces the synthesis of retinol-binding protein (RBP) and impairs enzyme function needed for vitamin A conversion.	Affects utilization and transport from the liver.
Chronic Alcoholism	Damages the liver and competes for enzymes involved in vitamin A metabolism.	Affects storage, metabolism, and mobilization.
Bariatric Surgery	Alters the structure of the digestive tract, reducing the area for absorption.	Primarily impairs absorption from the diet.
High Vitamin D Intake	Excessive vitamin D can increase the risk of vitamin A deficiency.	May affect bioavailability and metabolism.
Inadequate Dietary Fat	Without fat, the body cannot absorb fat-soluble vitamin A effectively.	Primarily impairs absorption from the diet.
Genetic Mutations	Variations in genes like BCO1 or RBP4 can reduce conversion or transport efficiency.	Affects metabolism, conversion, and transport.

Conclusion

Numerous factors beyond a simple lack of vitamin A-rich foods can lead to deficiency. While malnutrition is a significant cause globally, especially in vulnerable populations, underlying health conditions like celiac disease, cystic fibrosis, and liver disease are major drivers of depletion in developed countries. Chronic alcohol use, nutrient deficiencies (particularly zinc), and certain medications can also negatively impact vitamin A levels. Moreover, genetic predispositions can influence an individual's ability to absorb and utilize vitamin A efficiently. A comprehensive understanding of these complex interactions is essential for both prevention and treatment. For those with chronic illnesses or restrictive diets, working with a healthcare professional to monitor levels and consider supplementation is a proactive approach to maintaining this crucial nutrient.

Dietary Reference Intakes for Vitamin A

Frequently Asked Questions

What is the most common cause of vitamin A deficiency globally?

Globally, especially in developing countries, the most common cause is inadequate dietary intake due to malnutrition and limited access to foods rich in vitamin A.

How does liver disease lead to vitamin A deficiency?

The liver is responsible for storing most of the body's vitamin A. Diseases that compromise liver function, such as cirrhosis, impair the liver's ability to store the vitamin and to produce the transport proteins necessary to distribute it throughout the body.

Can taking a high dose of another vitamin lower vitamin A?

Yes, excessive intake of vitamin D, particularly in supplement form, can increase the risk of vitamin A deficiency. Excessive intake of synthetic beta-carotene supplements can also reduce vitamin A status.

Why is fat important for vitamin A levels?

Vitamin A is a fat-soluble vitamin, meaning it requires dietary fat for proper absorption in the small intestine. Following a severely restrictive low-fat diet can inhibit this process and lead to depletion over time.

How do genetic factors influence vitamin A levels?

Genetic variations can affect the efficiency of critical metabolic steps, such as the conversion of plant-based beta-carotene into active vitamin A or the transport of the vitamin from the liver to tissues. Individuals with certain variants may have a harder time maintaining adequate levels.

Can infections cause vitamin A deficiency?

Yes, infections can rapidly deplete vitamin A reserves as the body uses more of the vitamin to support its immune response. This creates a cycle where deficiency increases the risk of infection, and infection worsens the deficiency.

Are vegans at higher risk for vitamin A deficiency?

Vegans rely on provitamin A carotenoids from plants. Their risk can be higher if their diet is not carefully planned to include sufficient sources or if they have genetic variations that make the conversion to active vitamin A less efficient.